1. Field of the Invention
The present invention relates to a communication device comprising a carrier sense function and a communication method.
2. Description of the Related Art
A wireless LAN communication conforming to the IEEE 802.11 standards (for example, IEEE 802.11a/b/g/n) executes a random access based on carrier sense multiple access/with collision avoidance (CSMA/CA). For this reason, the arrival time of a received frame is unknown, and basically, a terminal always executes a frame detection operation.
According to the wireless LAN communication, it is difficult to fully avoid a frame error detection (i.e., a frame does not arrive; nevertheless, the frame arrival is detected) due to an influence of a thermal noise of the self-station, or an electric noise of a peripheral apparatus.
According to the IEEE 802.11 standards, when a frame is detected, it is determined that a carrier exists, and transmission is prohibited and the value of a counter waiting a transmission opportunity is cleared. For this reason, the frame error detection is a major factor in losing a transmission opportunity.
For example, Reference 1 (Jpn. Pat. Appln. KOKAI Publication No. 08-019030) discloses a technique of performing accurate carrier sense without receiving an influence of a noise generated by the device itself before wireless transmission starts.
According to the technique disclosed in the Reference 1, when a communication is executed, a control circuit operates a timer circuit for fixed time and the control circuit itself is changed in a suspended state. When a time out is occurred by the timer circuit, an interruption is executed for the control circuit, and the control circuit restarts. The control circuit executes a carrier sense using a wireless controller after it restarts. The Reference 1 discloses a technique that a determination of clear channel assessment (CCA) is not executed in the transmission timing because of a determination mistake being determined that a carrier exists though the carrier does not exist is often occurred in the transmission timing.
In contrast, Reference 2 (Jpn. Pat. Appln. KOKAI Publication No. 06-164444) discloses a technique that a CCA determination is not executed in the built-in DRAM refresh timing because of a determination mistake being determined that a carrier exists though the carrier does not exist is often occurred in the built-in DRAM refresh timing.
However, according to the Reference 1 and 2, it is difficult to avoid an error detection basis of a thermal noise and an unwanted radiation electric wave except the self-station.